Nonmacrocyclic Iron(II)Soluble Redox Mediators Leading to High-Rate Li-O_(2)Battery

The lithium-oxygen(Li-O_(2))battery is highly promising but suffers from poor cycling life,especially at high rates;hence,the need for high-efficient accelerating agents is crucial.Recently macrocyclic Fe-based redox mediators,such as iron(II)phthalocyanine(FePc)and heme,have been developed and anticipated to be ideal due to their bifunctional charge and superoxide shuttling capabilities.However,they still operate far below expectations,which could result from the low concentrations in electrolyte due to the strongπ-πinteraction at carbon cathode.Herein,the authors report a new type of nonmacrocyclic Fe-based redox mediators,iron(II)acetylacetonate[Fe(acac)2]and iron(II)glycinate[Fe(gly)2],which have weakπ-πinteraction with the carbon cathode,thus,remain at high concentrations in the electrolyte.The Fe(gly)2@Li-O_(2)battery reaches a long life of 321 cycles at 0.5 A g^(−1),which is much superior to the counterpart with the typical macrocyclic FePc,and particularly exhibits a long life of 167 cycles at 2.0 A g^(−1)and 136 cycles at ultrahigh 5.0 A g^(−1).This study demonstrates an efficient strategy to achieve a high-rate performance of Li-O_(2)batteries by developing nonmacrocyclic Fe-based redox mediators with high-efficient electron and superoxide shuttling.